What’s My Age Again: Why Mental Age Theory Hurts People with Intellectual and Developmental Disabilities

“Difficulty doing specific tasks isn’t the same thing as being an actual child. … I not mentally 12. I am mentally 28. I just have an intellectual disability.” -Ivanova Smith, adult with an intellectual disability
“You can support people without condescending to them. … Yes, I’m an adult. That doesn’t mean that I don’t have support needs. Rather, it means I should be able to share what my support needs are and direct the means by which I receive support.” Finn Gardiner, adult with a developmental disability

At least one form of discrimination in our society is alive and well. We discriminate against young people, every day, in policy and in practice. For example, in the United States, we don’t let people drive a car until they’re 16, vote until they’re 18, or buy alcohol until they’re 21. We deny freedoms to our citizens based on age alone, and it’s not even very controversial.

I’m not going to challenge age minimums in this post. I’m just using this as an example to shed light on a more problematic form of discrimination related to perceived age. This is the infantilization of adults with intellectual and developmental disabilities (IDD), based on a concept called “mental age.” Like chronological age, people use “mental age” as a shortcut to judge the maturity and competency of others, but the consequences of judging people by their “mental age” can be far more serious.

The concept of “mental age” was first introduced by Alfred Binet, co-creator of the first IQ tests, in the early twentieth century. Generally, “mental age” has been measured by comparing an individual’s score on a standardized IQ test with the average performance of their same-age peers. For people with IDD, “mental age” may also be estimated by comparing the person’s demonstrated physical, speech, adaptive or cognitive skills against the average for various age groups.

Not surprisingly, “mental age” came about alongside the eugenics movement in the United States. Mental ages were used to classify various groups of “feebleminded” individuals by severity: Adults with a mental age of 9-12 years were classified as “morons”; those with a mental age of 6-8 years were classified as “imbeciles”; and those with a mental age of 2-5 were classified as “idiots.” Individuals from any of these groups were thought unfit to reproduce.

Besides the disturbing history of mental age theory, using mental ages to classify individuals is problematic because:

First, mental age oversimplifies: Boiling an individual’s intellectual, developmental and adaptive functioning down to a single number obscures that person’s complexity. Some individuals may be highly skilled or knowledgeable in some areas, but experience impairments or naivete in others. Tests that measure only one or a few kinds of intelligence can miss other kinds of intelligence or compensatory skills that the individual uses. Intelligence test scores can also be biased by social and cultural factors unrelated to actual intelligence or skills.

Second, mental age is treated as a ceiling: Chronological age is, by definition, a dynamic concept. People are constantly aging, and this is part of the reason why age minimums are considered relatively acceptable in society: They are temporary. Eventually, everyone will get old enough to drive, vote, or buy a drink. In contrast, though, mental age is often described as a limit that someone reaches and cannot exceed. An adult with IDD may be labeled as having a mental age of 3, 7, or 10 years old, and once that mental age is reached, they are expected to think and act that way for the rest of their life. For example, in the 2001 film I Am Sam, the protagonist-a single father-is labeled with a mental age of 7. It is strongly implied that he will no longer be a fit dad after his child turns 8 because his daughter will continue developing while his development is locked. Although adults with IDD may reach plateaus in certain skills, everyone has the potential to adapt or improve their life circumstances. There have been powerful stories of adolescents or adults with severe communication impairments, for example, who showed great leaps in communication skills when presented with the right technology, the right support person, or both. Oftentimes it was discovered that these individuals had knowledge or skills that they had been unable to express to others in the past. Mental age labels artificially restrict that growth process. (Ironically, Alfred Binet himself believed that intelligence could change over a person’s life, but the IQ tests he helped design have been taken out of that context).

Most important, mental age is used to control freedoms and support: Outside the disability space, we understand that younger children usually need more support than older children and adults. We also reserve some freedoms (like driving, voting or buying alcohol) exclusively for older teens and adults. In the disabled world, too, presumed mental ages are used to deny freedoms. Even if a teen or adult with IDD is not explicitly labeled with a mental age, the prevailing belief that people with IDD are childlike leads too many parents and educators to infantilize them. For example, Finn Gardiner writes:

Infantilisation is very familiar issue to me. I myself have a developmental disability and my parents—my father in particular—infantilised me as a teenager and as a young adult. I wasn’t allowed to do what many of my peers were allowed to do; my parents claimed that I ‘wasn’t ready’ for many of the things everyone else my age seemed to be allowed to do, like going to school dances. My parents restricted what I read, thinking that I wasn’t mature enough to handle heavier themes in books, TV and films despite encountering similar subject matter in my assigned readings at school. They would force me to attend church even when I’d told them clearly that I was no longer religious; they justified this by claiming ‘in our house, we serve the Lord’, even though I was only going through the motions of practising Christianity. … When I was nineteen years old, my parents installed parental controls on my Windows account. … I was old enough to vote. In fact, I had voted when I was eighteen; I distinctly remember being eager to vote against George W Bush in 2004. My parents didn’t always give me the right to try, or if they did, they would do it begrudgingly and blame me if whatever I tried didn’t work out, instead of listening to me and working with me to identify strategies that did work for me. For them, supporting me entailed controlling me.

As Finn points out, these actions are not just insulting and frustrating, but could also be dangerous. A teen or adult with an IDD still has desires concomitant with their chronological age, including a desire for autonomy. An individual who has been infantilized may gravitate toward peers who seem to respect their autonomy. If that same individual has never been educated about sex, drugs, or other issues relevant to their chronological age, they could be an easy target for abuse and exploitation.

And, age can be used as a weapon in reverse, too. An adult with IDD may be denied supports due to their age, or admonished to “act their age” during a public meltdown, for example. But, many nondisabled adults have meltdowns, too. (We might see one on the floor of Congress today). Being an adult does not mean one lacks support needs, just as having support needs does not mean one is essentially a child.

So, how do we combat thinking based on mental age theory?

First and foremost, we need to separate maturity from support needs. Ivanova Smith suggests some ways in which we can concisely describe another person’s support needs without any reference to mental ages. For example:

Ivanova can’t drive due to developmental disability that causes them to have struggles with multitasking and hand eye cordination.
Ivan needs help across busy streets because they don’t understand traffic very well and need support to be safe.
Ivan may need support with emotional regulation because they process emotions differently than other people.

In a related vein, disabled children often receive primary support for disability-related needs from their parents or other family caregivers. Once these children become adults, they may still need human supporters, but having a parent continue to be the disability-related support worker can become a conflict of interest. When parents support their children, they hold authority in the relationship, but when disabled adults get support from people like readers, sign language interpreters or personal care assistants, they benefit from being the one in charge of the interaction. For example, when I was a child, my parents read to me often. They controlled what, when, and where the reading took place, which was entirely appropriate when I was a small child. As an adult, I still need human assistance accessing print, but I need to be the one in charge of what is being read to me. It can be difficult for a parent and adult child to renegotiate a supporting relationship in such a way that the parent is essentially working for their adult child (even if unpaid). It is important for adults with IDD to have self-determination, to the greatest extent possible, in directing who will support them, with what, when and where this support will occur. Depending on the resources available to that individual, and their specific impairments, family members may need to be involved with some of that process. This can work, but only if the family member(s) are willing to consider the disabled adult as someone with their own voice in decisionmaking.